In a supercharged internal combustion engine, in general, a turbocharger turbine is arranged in the exhaust passage at the upstream side from the catalyst, so the length of the exhaust passage from the exhaust port to the catalyst of the internal combustion engine becomes longer than that of a natural intake type internal combustion engine. Further, due to the increase in length of the exhaust passage and the presence of the turbocharger, the heat capacity of the exhaust system increases and the heat radiating surface area increases. For this reason, in a supercharged internal combustion engine, the temperature of the exhaust gas from the internal combustion engine ends up dropping until reaching the catalyst. In particular, after the cold start of an internal combustion engine, it takes time for the catalyst to warm up (that is, for the temperature of the catalyst to rise to the activated temperature), so deterioration of exhaust emission is liable to occur.
Further, as a method for dealing with this problem, a method is known of providing an exhaust bypass passage for bypassing the turbocharger turbine and an exhaust bypass valve opening/closing the exhaust bypass passage and, when the catalyst should be warmed up, making the exhaust gas bypass the turbocharger turbine so as to feed high temperature exhaust gas to the catalyst (for example, see Japanese Patent Publication (A) No. 2001-107722).